1. Technical Field of the Invention
The present invention relates to such a processing apparatus for a lithographic printing plate that is particularly effective for processing a lithographic printing plate having an image formed with a high definition AM screen or an FM screen. More specifically, the invention relates to a processing apparatus for a lithographic printing plate containing a photothermal conversion agent and being exposed with laser in a heat mode.
2. Description of the Related Art
In general, a photosensitive lithographic printing plate is developed with a photosensitive lithographic processing apparatus (hereinafter, sometimes referred to as a printing plate processor). The developing process in the printing plate processor is carried out in such a manner that a photosensitive lithographic printing plate having an image recorded therein is immersed in a developing solution retained in a developing bath by conveying the printing plate to the developing bath, and the photosensitive layer in an area having no image formed of the photosensitive lithographic printing plate is removed by a scrubbing means, such as a rotating brush roller, provided in the developing solution. In the printing plate processor, the photosensitive lithographic printing plate having been subjected to the developing step with the developer solution is rinsed with rinsing water in a rinsing part (rinsing step), and then subjected to a moistening treatment by coating a gum solution in a moistening part. The rinsing part contains feeding and ejecting rollers and a spray pipe, and the lithographic printing plate is rinsed by spraying rinsing water thereon from the spray pipe after passing through the feeding rollers.
In recent years, the prepress systems including a thermal plate is becoming to handle high definition images, and high definition images having a large halftone dot line number with an AM screen and image patterns with a small minimum pixel size with an FM screen are being brought into the market.
As the photosensitive lithographic printing plate, a conventional negative or positive printing plate has been used, but according to the progress of a computer-to-plate (CTP) system in recent years, systems using a photopolymer plate or a thermal plate are frequently employed. In particular, a thermal plate exposed in a heat mode is significantly advanced. It is disclosed in, for example, JP-A-2003-5379 and JP-A-2003-107684 as a related art.
However, the rinsing water is discharged from the spray pipe in the rinsing part hits against the upper and lower rollers at the feeding part of the rinsing part, and runs around the rollers to intrude into the side of the developing part, and as a result, the rinsing water is accumulated in the meniscus of the feeding rollers. Upon carrying on the lithographic printing plate from the developing part to the rinsing part, there are cases where the rinsing water is carried onto the plate to cause dripping.
It has been known that the upper feeding roller in the rinsing part is generally provided with a liquid cutting member for cutting the rinsing water running around the upper roller, and for example, a metallic bar is provided. However, the lower roller is not provided with a liquid cutting member, and the rinsing liquid running around the lower roller causes dripping.
The development of the lithographic printing plate slightly proceeds until the printing plate is conveyed to the rinsing part although the developing solution is squeezed with squeezing rollers at the ejection port of the developing part.
In the case where dripping of the rinsing liquid occurs on the lithographic printing plate from the feeding rollers of the rinsing part to the side of the developing part, the development slightly proceeding is suppressed on the dripping part. As a result, the dripping part has a density different from the surroundings to cause image unevenness. In the case where a thermal positive plate is used, for example, the density on the dripping part is increased. In the case of a high definition AM screen image or FM screen image having a large circumferential length, the extent of image unevenness is further deteriorated due to the larger change in density on progress of development.
In particular, the thermal plate is liable to change in halftone dot area depending on the extent of development progress, and thus the image unevenness is liable to occur. Accordingly, it is necessary to effect a uniform developing treatment.